An ear thermometer has a probe provided with an infrared sensor. The probe is inserted into an ear and the ear thermometer can measure a body temperature within a short time such as one second. Accordingly, the ear thermometer is very useful to measure the body temperature of an infant or a child who easily cries, or is asleep, or keeps moving.
The body temperature measured by the ear thermometer is generally displayed with liquid crystal from viewpoints of small size, low power consumption, light weight, and the like. The liquid crystal displaying is acceptable in a bright place but it is hardly visible in a dark place. In particular, measuring the body temperature of an infant or a child is frequently carried out in a relatively dark place when the infant or child is sleeping. It is important, therefore, to make the displayed temperature visible even in a dark place.
To make the body temperature displayed with liquid crystal visible even in a dark place, irradiating the liquid crystal with backlight is effective. Irradiating liquid crystal with backlight, however, consumes large power. For example, the backlight for liquid crystal of the ear thermometer consumes 75% or more of total power consumption. This raises a necessity of increasing the capacity of a battery of the ear thermometer. For this, a conventional ear thermometer must increase a normally used button-type or AAA-size battery to two pieces.
As mentioned above, the conventional ear thermometer makes a body temperature displayed with liquid crystal visible even in a dark place by irradiating the liquid crystal with backlight. The backlight consumes large power, and therefore, needs to increase the number of batteries to use. This results in increasing the price, size, and weight of the ear thermometer, thereby deteriorating the usability of the ear thermometer. If the number of batteries is not increased, the large power consumption by backlight forces the battery to be frequently replaced with a new one, thereby deteriorating the usability and practicality of the ear thermometer.